hi folks, i have a fill valve (not an anti-siphon one) in my design connecting the domestic hot water supply, which isheated on demand, to the hot tub loop. the equipment is mounted lower than the tub will be installed. i put a brass swing check valve at the hot water supply, and of course the municipal water supply is at higher pressure than the head creates, but i don't know if this enough prevention for a prudent setup. i don't need one of those complicated RPBP units, i hope. if anyone with experience can comment i'd appreciate it. my several pool books don't address this question, maybe because most installs don't have filler valves. thanks!